Depending on the requirements for different display modes, in a liquid crystal display using nematic liquid crystal, the alignment of the nematic liquid crystal between substrates has different manors. Generally, there are two alignment manors of nematic liquid crystal: nematic liquid crystal planar-alignment mode and nematic liquid crystal vertical-alignment mode.
When the display mode is TN (twisted nematic, (orientation of liquid crystal molecules form a 90-degree twist)), STN (super twisted nematic, a 180-degree twisted nematic), IPS (in-plane switching), FFS (fringe field switching) or the like, a planar-aligning method is adopted to induce the alignment of nematic liquid crystal. For example, a preparation method is as follows.
1. An alignment layer is formed, by applying an aligning agent (for example, polyimide (PI) or polyvinyl alcohol (PVA)) on a surface of a substrate.
2. The alignment layer on a substrate surface is dried.
3. The substrate surface having the alignment layer is rubbed after the drying process, so that a plurality of microgrooves are formed on the substrate having the alignment layer.
4. Nematic liquid crystal is added dropwise on the substrate formed with grooves, and then a liquid crystal layer is sandwiched between two substrates after a liquid crystal cell is formed. Under the action of the alignment layer formed on the substrates, the nematic liquid crystal molecules are induced in an alignment.
When the display mode is MVA (multi-domain vertical-alignment), a different aligning agent may be adopted to induce the alignment of nematic liquid crystal. A preparation method for that aligning agent is substantially the same as the planar-aligning method; siloxane may be elected as the aligning agent for vertical-alignment; the silicone is applied on a substrate surface and then dried; silicone adheres to the substrate by chemical bonds, and the flexible chain groups at ends of siloxane are capable of inducing nematic liquid crystal in an arrangement perpendicular to the substrate.
The above are two common aligning methods for liquid crystal; they both achieve liquid crystal alignment through treatment onto a substrate surface. The alignment mechanism is that, by inducing the alignment of the liquid crystal which is close to a surface of an alignment layer, the nematic liquid crystal within the entirety of a liquid crystal cell is caused to be arranged. However, the alignment layer applied on a substrate has less action on the liquid crystal molecules far away from the alignment layer, so that the aligning action on the liquid crystal molecules is non-uniform, thereby affecting liquid crystal display effect.